LAOS Laser

Hi Paul,

This is not the easiest type of flow sensor you can connect. An easier type is the one where the water pressure closes a switch. Such a flow sensor can be connected in series with the door switch.

• connecting it via the optocoupler (is your zmin input still free?) and changing the firmware to read the pulses.
• make a small circuit that drives a relay/optocoupler/FET that can go in series with the door switch

Jaap

Jaap,
thanks for the reply, I think I prefer the seconds option - "make a small circuit that drives a relay/optocoupler/FET that can go in series with the door switch"

Would you have any idea where I could find such a circuit ?

Many thanks
Paul

Something like this?

Hi Jaap,
Am I correct in thinking that the components in your sketch are a capacitor and an Optocoupler IC ?
If so I have 8 spare Optocoupler KB847 that I bought when I got the components to assemble the LaOS Rev 5 board, would one of these be suitable ?

I can assemble the circuit on a piece of vero board, I think I have some cct board screw terminals left over from the Air Assist / Exhaust relay control board project, and I must have a suitable capacitor in my odds and sods box.

Once the circuit is built I assume that I cut one of the 'laser power button' feed wires and insert the right hand side of the circuit in to the cut wire.

Regards,
Paul

A KB847 contains 4 optocouplers, so that will work fine (and you have 3 left for other extensions). It would be even nicer if there's also a red led/piezo buffer to warn you why the laser is not firing. But the red light should be on when the water flow is off, so you need to invert the signal that you feed into the opto coupler...

Here is the circuit that I built to monitor the pulses coming from the hall effect flow sensor. It works a treat, the flow sensor is attached at the output of the laser tube cooling water just before it returns to the reservoir.
The basis of the circuit is a 555 timer in Monostable configuration, the flow sensor pulses when water is flowing, this pulse is used to constantly reset the 555 which is trying to reset on a 1 second interval. As long as the 555 never resets the relay is kept energised, if the pulses stop after a maximum of 1 second the 555 will reset and this will trigger the transistor and therefore power down the relay.
The relay is (a) switching a buzzer on/off and (b) making or breaking the laser power circuit. The LaOS board is still in control of the laser power supply, the relay can however break the circuit and therefore protect the laser tube in the event of cooling water flow failure. The buzzer will also sound until the flow of water is started, once the flow is present the buzzer will be silent unless the water flow is interrupted at which point the buzzer will sound and the laser power supply will be interrupted.
The circuit takes minimal power and is powered from the same PSU as the LaOS board is powered from.
The circuit cost under £5 to make and the flow sensor was a further £3 (with free delivery) so for under £10 I have piece of mind that the water flow is being monitored all the time the laser cutter is in use.
I bought the flow sensor from Newfrog.com I am in no way associated Newfrog, but can highly recommend them for being both very cheap, free delivery and good quality, have a look they sell all sorts.

If anyone needs any further info please ask :)

Regards,
Paul (Depronman)

Then let me add mine as well..:
I'm using an arduino. Which is a bit of an overkill, but considering you can get arduino clones for 5 euros (search ebay for Mini USB Nano) it's cheap and easy.

Connect yellow wire to pin 2. Pin 3 is pulled low when water is flowing, or is floating when no water. This connects straight to the safety input on my power supply (labeled P+) which should be pulled to ground for the laser to work.

Attached is the arduino sketch.

btw Jaap I think your circuit will not work; you'd need at least a series capacitor to filter out DC, followed by a diode to rectify the AC component.